Kristen Nagy, an 18-year-old from Sparta, N.J., sends and receives 500 text messages a day. But she never uses Twitter, even though it publishes similar snippets of conversations and observations.

“I just think it’s weird and I don’t feel like everyone needs to know what I’m doing every second of my life,” she said.

Her reluctance to use Twitter, a feeling shared by others in her age group, has not doomed the microblogging service. Just 11 percent of its users are aged 12 to 17, according to comScore. Instead, Twitter’s unparalleled explosion in popularity has been driven by a decidedly older group. That success has shattered a widely held belief that young people lead the way to popularizing innovations.